Most engine mounts are passive rubber components. The desire is to have stiff engine mounts during high speed/high torque operation to minimize the relative movement between the engine and the vehicle frame to minimize stress on exhaust joints. During low speed engine operation, a softer engine mount is desired to avoid transmitting engine vibrations to the vehicle frame and to vehicle occupants. If vibration is transmitted to the vehicle frame, it may become a source of customer dissatisfaction. Unfortunately, during cold start, the rubber engine mount is cold and at its stiffest. And, during cold start, this is typically a time when the engine is operating at low speed when a softer engine mount is desired. When the engine compartment warms up, the engine mount also warms up and becomes softer, which is when a stiffer mount is desired.
Another passive engine mount is a hydraulic mount in which damping is provided by a hydraulic fluid that passes through an orifice. Hydraulic mounts suffer from the same problem as rubber mounts due to the hydraulic fluid in the engine mount being colder and thus more viscous at low temperatures, i.e., stiffer damping. When warm the hydraulic fluid is less viscous and provides less damping.
Some engines are equipped with cylinder deactivation so that at low torque demand, the valves are deactivated in some number of cylinders so that the cylinders continuing to operate are at a higher torque, higher efficiency operating condition to thereby reduce fuel consumption. In cylinder deactivation mode, the firing frequency of the engine is reduced and is possibly uneven, leading to vibration transmission to the vehicle frame. In vehicles equipped with cylinder deactivation, it is common to delay cylinder deactivation until the engine mounts are sufficiently warmed up after a cold start to avoid undesirable transmission of vibration to vehicle occupants. Unfortunately, right after cold start is often a time when cylinder deactivation would provide a desirable boost in operational efficiency.
Some engine mounts are tunable or active. The hydraulic mount can have a valve to control the ease with which the hydraulic fluid moves between chambers and thus the damping. Other examples include electrorheological and magnetorheological fluids in engine mounts. When a stiffer mount is desired, an electric current or magnetic field, respectively, is applied to cause the fluid to become more viscous and stiffen. Such active engine mounts are soft at idle when the fluid is at operating temperature. However, during cold start operation, the un-warmed fluid can be more viscous than desired transmitting too much vibration to the vehicle occupants and not allowing cylinder deactivation.
In prior art KR20120069918, a resistance heater is disposed in the engine mount. The heater is coupled to and powered by the engine's battery to preheat the engine mount prior to engine starting. Such a system relies on the engine battery for preheat, thereby discharging the battery and impairing the battery's ability to crank the engine during the cold start, the greatest demand on the battery. A way to preheat the engine mount without draining the vehicle battery is desired.